Vehicle coolant pumps, generally referred to as water pumps, incorporate a spring loaded face seal that sees very high temperatures, speeds and sealing forces, and which is consequently highly prone to wear if it is out of tolerance or distorted in any way. A common type of face seal has one sealing ring that is a single piece of bronze, ceramic or other wear and heat resistant material, which can be lapped very flat. It is contacted by another sealing ring, under a high spring force, at an interface that constitutes a primary barrier to coolant linkage. For that interface to stay tight, the mated faces must be, and must remain, substantially flat. To reduce wear, it is common to make one of the sealing rings as a composite structure with a main body that is a graphite and phenolic resin mix. An annular bronze insert is molded into the main body, concentric therewith. When the composite sealing ring is machined flat, the result is a sealing face that has two concentric annular areas, an outer annulus of bronze and an adjacent inner annulus of the graphite resin mix. The bronze provides toughness and high wear resistance. The molded graphite and resin body holds the insert and acts to continually leach some of its graphite onto and into the sealing interface, lubricating and reducing wear. The combination of qualities provided is very beneficial.
The composite structure also causes a problem, however. In order to facilitate the bond between the molded main body and the bronze insert, the bronze insert has a series of evenly circumferentially spaced teeth and slots cut into it. The molded phenolic mix flows in and around the slots, creating a strong adhesion. It was discovered that in-use, the graphite phenolic mix, which is porous, was absorbing the ethylene glycol and water coolant, causing it to swell. The non-porous bronze absorbed essentially none. The differential absorption and swelling was translated by the slots and teeth into a regular, almost sinusoidal peak and valley pattern of distortion on the face of the sealing ring. Though slight, even a slight distortion can lead to lessened seal life. While incipient leakage is not severe, and the seals can be easily replaced before there is a real problem, longer lasting parts are always desirable.